This invention relates to pallets and slip sheets, and more particularly to an improved slip sheet.
Material handling apparatus for industrial use is commonly designed for ease of storage and handling in a warehouse and shipping on truck or rail. Different kinds of containers for various types of goods, for example cases of beer, are commonly arranged in a generally cubical array and are supported on a pallet. The array and pallet may then be lifted by a lift truck and stacked upon another array of containers for conservation of storage space. The array and pallet may also be conveniently loaded and unloaded for shipping in trucks, railcars, ships and other transport means.
Commonly used pallets are constructed from wood with two planar support surfaces separated by spaced rails. The support surfaces have the general size and shape of the array to be supported, and the pallet is about 5 1/2 inches thick. The pallet and array of containers are lifted and moved by inserting the forks of a forklift between the vertically separated support surfaces and the horizontally spaced spacer rails. Wood pallets are relatively expensive. Furthermore, the thickness of these pallets takes up useful storage space and their weight adds to transportation expense.
These problems have been somewhat overcome by the development of slip sheets, also referred to as slip sheet pallets or slip pallets. A typical slip sheet comprises a relatively thin sheet of a material, such as chipboard or plastic, for supporting the array of containers. The array and slip sheet are lifted by gripping a lip portion extending from an edge of the slip sheet and holding it under tension with a lift truck gripping mechanism while slipping a platen (a spatula like member) of the lift truck under the slip sheet. The platen is raised to lift the array and slip sheet and the lift truck then moves them to a desired location where the slip sheet and the array are pushed off of the platen. Although slip sheets offer various advantages over common wooden pallets, some problems have been found in their use. Unlike conventional wood pallets, slip sheets do not have a lower opening for insertion of a lift truck lifting platform. Sliding a platen under a slip sheet resting on a hard surface causes a deformation wave to pass through the slip sheet as the leading edge of the platen moves below it. One significant problem with simple slip sheets formed from a single layer of plastic or chip board has been that shock, vibration and deformation waves, encountered during lift truck handling or rail or truck transportation are transmitted through the slip sheet to the array causing damage to items in the array, particularly items stacked at the bottom of the array. For example bottom tier beverage cans are often damaged by such shocks or deformations. Attempts to provide slip sheets having cushioning and stiffening capabilities to resist such shocks and deformation waves have heretofore met with only limited success. In some cases the shock absorption capabilities have been too meager. In others the cost of producing such shock absorbing slip sheets has been too great and/or the size and/or weight of the shock absorbing slip sheet has been commercially unacceptable. Also, where shock absorption is achieved by making the slip sheet extremely flexible, damage caused by deformation waves has been exacerbated.
Some of the various types of pallets and slip sheets which have been employed in the past are disclosed in: U.S. Pat. No. 3,199,468 issued Aug. 10, 1965 for NESTABLE PALLETS of Sullivan; U.S. Pat. No. 3,545,249 issued Dec. 8, 1970 for DIMPLE AND METHOD OF FORMING SAME of Brown; U.S. Pat. No. 3,776,145 issued Dec. 4, 1973 for SLIP PALLET of Anderson, et al; U.S. Pat. No. 3,850,116 issued Nov. 26, 1974 for SLIP PALLET REINFORCED WITH FILLERS of Mackes; U.S. Pat. No. 4,042,127 issued Aug. 16, 1977 for SLIP PALLET AND DIVIDER SHEET of Brossia; U.S. Pat. No. 4,507,348 issued Mar. 26, 1985 for CORRUGATED BOARD-LIKE SHEET MADE OF SYNTHETIC RESIN of Nagata, et al; U.S. Pat. No. 4,562,718 issued Jan. 7, 1986 for PALLET AND METHOD OF PRODUCTION of Dunk; U.S. Pat. No. 4,906,510 issued Mar. 6, 1990 for METHOD AND APPARATUS FOR FORMING A HINGE FOR LAMINATED CORRUGATED MATERIAL of Todor, Jr., et al.; U.S. Pat. No. 5,226,372 issued Jul. 13, 1993 for SLIP PALLET WITH A CUSHIONING EFFECT of Frenkel, et al.; and German Patent No. 2625346 filed Jun. 4, 1976 for FLEXIBLE COMPONENT of Stangeland, et al. The above patents are each hereby specifically incorporated by reference for all that is disclosed therein.